Assertion (A) & Reason (B) MCQ

MCQ 11 Mark

Assertion: The time period of revolution of a satellite close to surface of earth is smaller than that revolving away from surface of earth.
Reason: The square of time period of revolution of a satellite is directly proportional to cube of its orbital radius.

A
Assertion and reason both are correct statements and reason is correct explanation for assertion.
B
Assertion and reason both are correct statements but reason is not correct explanation for assertion.
C
Assertion is correct statement but reason is wrong statement.
D
Assertion is wrong statement but reason is correct statement.

Answer

(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
Explanation: The time period of satellite, $T \propto r^{3 / 2}$
$
\text { or } T \propto\left(R_{e}+h\right)^{3 / 2}
$
For a satellite revolving close to surface of the earth, $h =0$.
$
\therefore T \propto\left(R_e\right)^{3 / 2}
$
It is evident that the period of revolution of a satellite depends upon its height above the earth's surface. Greater is the height of a satellite above the earth's surface greater is its period of revolution.

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MCQ 21 Mark

Assertion (A): A quick collision between two bodies is more violent than slow collision, even when initial and final velocities are identical.
Reason (R): The rate of change of momentum determines that the force is small or large.

A
Both A and R are true and R is the correct explanation of A.
B
Both A and R are true but R is not the correct explanation of A.
C
A is true but R is false.
D
A is false but R is true.

Answer

(a) Both A and R are true and R is the correct explanation of A .
Explanation: In a quick collision, time t is small. As $F \times t =$ constant. Therefore, force involved is large, i.e., collision is more violent in comparison to slow collision.

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MCQ 31 Mark

Assertion (A): Two vectors are equal when their magnitude and direction both are equal.
Reason (R): For any two vectors $\overrightarrow{ A }$ and $\overrightarrow{ B }$, if angle between them is $\frac{\pi}{4}$ rad, then $\overrightarrow{ A } \times \overrightarrow{ B }=\overrightarrow{ A } \cdot \overrightarrow{ B }$.

A
Both A and R are true and R is the correct explanation of A.
B
Both A and R are true but R is not the correct explanation of A.
C
A is true but R is false.
D
A is false but R is true.

Answer

(c) A is true but R is false.
Explanation: A is true but R is false.

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MCQ 41 Mark

Assertion (A): Efficiency of a Carnot engine increases on reducing the temperature of sink.
Reason (R): The efficiency of a Carnot engine is defined as ratio of net mechanical work done per cycle by the gas to the amount of heat energy absorbed per cycle from the source.

A
Both A and R are true and R is the correct explanation of A.
B
Both A and R are true but R is not the correct explanation of A.
C
A is true but R is false.
D
A is false but R is true.

Answer

(b) Both A and R are true but R is not the correct explanation of A .
Explanation: Efficiency of Carnot cycle $\eta=\frac{W}{Q_1}=1-\frac{T_2}{T_1}$, for carnot engine when $T _2$ decrease $\eta$ increase.

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Physics Assertion (A) & Reason (B) MCQ

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